docs: def _sia_cache_key(subsystem):
      """The cache key of the subsystem.
  
      This includes the native hash of the subsystem and all configuration values
      which change the results of ``sia``.
      """
      return (
          hash(subsystem),
          config.ASSUME_CUTS_CANNOT_CREATE_NEW_CONCEPTS,
          config.CUT_ONE_APPROXIMATION,
          config.MEASURE,
          config.PRECISION,
          config.VALIDATE_SUBSYSTEM_STATES,
          config.SINGLE_MICRO_NODES_WITH_SELFLOOPS_HAVE_PHI,
          config.PARTITION_TYPE,
      )